The present invention relates to a radial tire for heavy duty vehicles in which the wandering phenomenon can be effectively prevented.
While the vehicle on which the so-called heavy duty radial tires are mounted, such as truck, bus, light truck and the likes, is running on the road having various gradients on the surface in the lateral direction to the running direction of the vehicle, such as a rutted road, the wandering phenomenon is often experienced by the driver, especially when running at high spaced.
In general, radial tires are provided with a steel cord belt over the carcass to provide a hoop effect on the tire and to increase the rigidity of the tread region. Such belt reinforcement, however, increases the rigidity of both edge portions of the tread which has a great effect on the wandering phenomenon. Further, in the conventional radial tires, the outer periphery of the tread region, that is, the tread surface is formed in a smoothly curved profile all over the width. Accordingly, as exaggeratedly shown in FIG. 6, the tread surface A has non-contacting parts D in the vicinity of the tread edges. Such parts gradually extend away from the road surface C towards the axially outside due to the above-mentioned curvature, but its start point (B) is continually shifted irregularly while running on the road having various gradients on the road, surface, which creates irregular lateral forces on the tire, and the force act on the rigid tread edge portions. As the result, the wandering phenomenon of the vehicle is induced. On the basis of such understanding and discovery, the present invention was made.
It is therefore, an object of the present invention to provide a heavy duty radial tire whereby the wandering phenomenon can be effectively prevented.
According to one aspect of the present invention, a heavy duty radial tire is provided with
a tread surface defining a ground contacting area between the axially outer edges thereof and provided with at least one longitudinal groove extending in the circumferential direction of the tire, and a buffer plane extended radially inwardly from each of the axially outer edges of the tread surface so as to be formed substantially in part of a right circular cone having its axis placed on the tire axis, the buffer plane being provided with at least one buffer groove extending substantially continuously in the circumferential direction of the tire.